Jet engine parts are subject to extremely adverse conditions, such as dramatic temperature changes, constant and/or sudden vibration and the like. The jet engine parts, particularly the moving parts thereof, must be substantially defect free in order to satisfactorily withstand these conditions. Manufacture of the parts is therefore necessarily expensive, in view of the high degree of quality which must be maintained. Should a particular part not conform to the exacting standards specified and required, then it must be discarded or repaired, if possible.
The demands placed upon the jet engine parts has spurred a search for new, stronger and harder materials. One class of materials developed for this purpose is the nickel-based superalloys. These alloys typically contain in excess of 50% by weight nickel, and have varying concentrations of alloying elements to carefully tailor the properties of the resulting matrix. A particular super alloy of interest is Inconel R 713, a precipitation hardenable alloy used in the manufacture of turbine parts. This alloy utilizes aluminum and titanium as alloying elements, and the cast form of the alloy is known as 713C.
A particular problem with the precipitation hardenable alloys, such as Inconel 713, is the inability to weld these materials with a like material for purposes of repair, and the like. Welding, because of the high temperatures involved, has a tendency to cause cracking at the area of the weld site, thereby resulting in destruction of the welded parts. The crack formations is believed to be due to the formation of gamma-prime, a phase of the alloy resulting from the aluminum and titanium addition. Attempts have been made to weld Inconel 713 with other nickel-based alloys, but these other alloys tend not to have the appropriate characteristics required, and this solution is therefore marginal, at best.
From the above, it can be seen that there is a need for a process permitting precipitation hardenable alloys to be welded with other elements of like alloy composition. Such a process would permit parts having relatively minor defects to be repaired, thereby making the manufacturing process more efficient.
The disclosed invention is a process for welding nickel alloy substrates having a gamma-prime phase with a like alloy, typically with an alloying powder. The welding process utilizes the radiation from a laser beam to form a relatively small molten pool of the alloy substrate. The alloying powder is dispersed within the pool. Movement of the beam relative to the pool causes the pool to rapidly solidify. In this way, the cooling pool rapidly falls through the gamma-prime temperature formation range so that little or no additional gamma-prime is formed in the area of the weld site.